1. Field of the Invention
The present invention relates to an image display apparatus or the like that displays a blood flow in an ultrasonic diagnostic apparatus, and more particularly, to an image display apparatus involving a B-mode method (tomogram display).
2. Description of the Related Art
The ultrasonic diagnostic apparatus is to display a tomogram based on an ultrasonic signal reflected from an object body, and a method of displaying the tomogram in real time is referred to as a B-mode method.
The B-mode method has a disadvantage in that, while it allows tissues of the object body to be displayed with good quality, when displaying a blood flow in a blood vessel, the image thereof becomes blurred. To overcome the disadvantage, an attempt involving a digital technology has been made as follows. FIG. 10 illustrates an operation of a method of displaying a blood flow in the conventional ultrasonic diagnostic apparatus. This is referred to as a B-Flow, which is disclosed in the web site of http://www.gemedicalsystems.com/rad/us/education/msutut4.html.
With reference to FIG. 10, the operation of the conventional ultrasonic diagnostic apparatus will be described below. First, an encoder 20 emits an ultrasonic beam. The ultrasound reflected from a human body 2 (referred to as an echo, hereinafter) is decoded in a decoder 21, and then displayed in B-mode.
Here, as shown in FIG. 16, a blood flow 161 lies deeper in the object body than a tissue 160. Thus, for an incident ultrasonic beam 162, a blood flow echo 163b and a tissue echo 163a return with a time lag, so that the two echoes can be distinguished. Since the blood flow echo is weaker than the tissue echo, the sensitivity is enhanced when receiving the blood flow echo. The time lag between the reflection echoes is due to a fact that the tissue echo is contributed by a reflection from a blood vessel wall and the blood flow echo is primarily contributed by a scattering from a red blood cell in the blood vessel. The encoder 20 and the decoder 21 are used to distinguish and superimpose the weak reflection echoes. That is, according to an encoded pattern, signals received at the timing of xe2x80x9c1xe2x80x9d are added, and the result is regarded as the received echo. Strictly speaking, the reflection echo due to the thickness of the tissue 160 includes echoes from a tissue surface and from an interface with the blood flow. For simplicity, however, only the latter is shown in FIG. 16.
According to the above arrangement, however, the blood flow echo and the tissue echo are distinguished based on the time lag therebetween, and thus, cannot be separated if they are close to each other. That is, it is difficult to display the blood flow near the blood vessel wall or the blood flow in a thin blood vessel. In addition, since the blood flow echo and the tissue echo are close to each other, it is difficult to adjust the amplification factor thereof. For example, if the amplification factor is enhanced to be adapted for the blood flow, there is a possibility that the whole image becomes too bright, and a whitish image is provided.
In short, with the conventional ultrasonic tomography, when a tomogram for the whole object body is generated in B-mode, a vivid image of the blood flow cannot be produced.
There is another approach of utilizing the Doppler effect to derive from the received ultrasonic signal a phase difference between a wave reflected from the blood flow and a wave reflected from the tissue, calculating velocity data of a section of the blood flow, that is, direction and intensity data thereof based on the phase difference, generating a color image reflecting the velocity of the flow, and superimposing the color image on the B-mode image for display. This approach is referred to as Color Flow, and is disclosed in xe2x80x9cBasic Ultrasonic Medicinexe2x80x9d (Ishiyaku Publishing Inc.), p. 55-57 and U.S. Pat. No. 4,622,977, for example. The entire disclosure of the each publication is incorporated herein by reference in its entirety.
However, the Color Flow requires dedicated image processing means that involves an enormous amount of complicated calculation such as an autocorrelation operation or fast Fourier transform, and thus, the whole apparatus is complicated and the cost is increased. Furthermore, the Color Flow cannot provide an actual image of the blood flow, so that the image provided is poor in reality.
In view of the problems described above, this invention aims to provide an ultrasonic tomography apparatus and an ultrasonic tomography method that can, with a simple and inexpensive arrangement, display an image of a tissue and blood flow in an object body in B-mode such vividly that they can be easily distinguished.
One aspect of the present invention is an ultrasonic tomography apparatus, comprising:
ultrasonic transmitting means of transmitting an ultrasound to an object body;
ultrasonic receiving means of receiving the ultrasound reflected from said object body and producing an ultrasonic signal;
filtering means of extracting components of said ultrasonic signal in at least two different frequency bands; and
image generating means of generating an ultrasonic tomogram of said object body based on said extracted ultrasonic signal component in a first frequency band and said extracted ultrasonic signal component in one or more second frequency bands,
wherein said first frequency band centers on a frequency band at the time of said transmission, and
said second frequency band is shifted from the frequency band at the time of said transmission.
Another aspect of the present invention is an ultrasonic tomography apparatus, comprising:
ultrasonic transmitting means of transmitting an ultrasound to an object body;
ultrasonic receiving means of receiving the ultrasound reflected from said object body and producing an ultrasonic signal;
filtering means of extracting components of said ultrasonic signal in at least two different frequency bands; and
image generating means of generating a first partial ultrasonic tomogram of said object body based on said extracted ultrasonic signal component in a first frequency band and a second partial ultrasonic tomogram of said object body based on said ultrasonic signal component in one or more second frequency bands,
wherein said first frequency band centers on a frequency band at the time of said transmission, and
said second frequency band is shifted from the frequency band at the time of said transmission.
Still another aspect of the present invention is the ultrasonic tomography apparatus further comprising:
image processing means of performing an image processing on at least one of said first partial ultrasonic tomogram and said second partial ultrasonic tomogram; and
image synthesizing means of producing an ultrasonic tomogram by performing any of (1) synthesis of the first partial ultrasonic tomogram subject to said image processing and the second partial ultrasonic tomogram not subject to said image processing, (2) synthesis of the first partial ultrasonic tomogram not subject to said image processing and the second partial ultrasonic tomogram subject to said image processing, and (3) synthesis of the first partial ultrasonic tomogram subject to said image processing and the second partial ultrasonic tomogram subject to said image processing.
Yet still another aspect of the present invention is the ultrasonic tomography apparatus, wherein said second frequency band is set centering on a frequency for which a signal component having a level more than predetermined one is detected by scanning a predetermined bandwidth allowing for a potential Doppler shift from said first frequency band.
Still yet another aspect of the present invention is the ultrasonic tomography apparatus, wherein said second frequency band is set centering on a frequency for which a signal component having a level more than predetermined one is detected by frequency-analyzing said received reflected ultrasonic.
A further aspect of the present invention is the ultrasonic tomography apparatus, wherein said filtering means includes:
a first sub-filter for allowing said first frequency band to pass therethrough; and
one or more second sub-filters for allowing said second frequency band to pass therethrough.
A still further aspect of the present invention is the ultrasonic tomography apparatus, wherein said filtering means is set a first pass band for allowing said first frequency band to pass through the filtering means and a second pass band for allowing said second frequency band to pass through the filtering means, and
said first pass band and said second pass band allow signals to pass therethrough simultaneously.
A yet further aspect of the present invention is the ultrasonic tomography apparatus, wherein said filtering means allows said first frequency band or said second frequency band to pass therethrough selectively, and
said image generating means performs an operation using the ultrasonic signal component in said first frequency band and an operation using the ultrasonic signal component in said second frequency band in a time-divisional manner.
Still yet further aspect of the present invention is the ultrasonic tomography apparatus, wherein in said filtering means, the number of times of selection of said second frequency band is higher than that of said first frequency band.
An additional aspect of the present invention is the ultrasonic tomography apparatus, wherein said image generating means includes amplifying means of amplifying a signal having passed through said first frequency band and/or a signal having passed through said second frequency band, and
said amplifying means amplifies the signal having passed through said second frequency band more than the signal having passed through said first frequency band.
A still additional aspect of the present invention is the ultrasonic tomography apparatus, wherein said object body is a human body,
said first frequency band is a frequency band of an echo from a tissue of said human body, and
said second frequency band is a frequency band of an echo from a blood flow in said human body.
A yet additional aspect of the present invention is the ultrasonic tomography apparatus, wherein said filtering means includes:
a first sub-filter for allowing said first frequency band to pass therethrough; and
one or more second sub-filters for allowing said second frequency band to pass therethrough.
A still yet additional aspect of the present invention is the ultrasonic tomography apparatus, wherein said filtering means is set a first pass band for allowing said first frequency band to pass through the filtering means and a second pass band for allowing said second frequency band to pass through the filtering means, and
said first pass band and said second pass band allow signals to pass therethrough simultaneously.
A supplementary aspect of the present invention is the ultrasonic tomography apparatus, wherein said filtering means allows said first frequency band or said second frequency band to pass therethrough selectively, and
said image generating means performs an operation using the ultrasonic signal component in said first frequency band and an operation using the ultrasonic signal component in said second frequency band in a time-divisional manner.
A still supplementary aspect of the present invention is the ultrasonic tomography apparatus, wherein in said filtering means, the number of times of selection of said second frequency band is higher than that of said first frequency band.
A yet supplementary aspect of the present invention is the ultrasonic tomography apparatus, wherein said image generating means includes amplifying means of amplifying a signal having passed through said first frequency band and/or a signal having passed through said second frequency band, and
said amplifying means amplifies the signal having passed through said second frequency band more than the signal having passed through said first frequency band.
A still yet supplementary aspect of the present invention is the ultrasonic tomography apparatus, wherein said object body is a human body,
said first frequency band is a frequency band of an echo from a tissue of said human body, and
said second frequency band is a frequency band of an echo from a blood flow in said human body.
Another aspect of the present invention is an ultrasonic tomography method, comprising the steps of:
transmitting an ultrasound to an object body;
receiving the ultrasound reflected from said object body;
extracting components of said ultrasound in at least two different frequency bands; and
generating an ultrasonic tomogram of said object body based on said extracted ultrasonic component in a first frequency band and said extracted ultrasonic component in one or more second frequency bands,
wherein said first frequency band centers on a frequency band at the time of said transmission, and
said second frequency band is shifted from the frequency band at the time of said transmission.
Still another aspect of the present invention is an ultrasonic tomography method, comprising the steps of:
transmitting an ultrasound to an object body;
receiving the ultrasound reflected from said object body;
extracting components of said ultrasonic in at least two different frequency bands;
generating a first partial ultrasonic tomogram of said object body based on said extracted ultrasonic signal component in a first frequency band; and
generating a second partial ultrasonic tomogram of said object body based on said extracted ultrasonic signal component in one or more second frequency bands,
wherein said first frequency band centers on a frequency band at the time of said transmission, and
said second frequency band is shifted from the frequency band at the time of said transmission.
Yet still another aspect of the present invention is the ultrasonic tomography method, wherein said second frequency band is set centering on a frequency for which a signal component having a level more than predetermined one is detected by scanning a predetermined bandwidth allowing for a potential Doppler shift from said first frequency band.
Still yet another aspect of the present invention is the ultrasonic tomography method, wherein said second frequency band is set centering on a frequency for which a signal component having a level more than predetermined level is detected by frequency-analyzing said received reflected ultrasonic.